U.S. patent number 5,919,543 [Application Number 08/912,159] was granted by the patent office on 1999-07-06 for composite sine wave spar.
This patent grant is currently assigned to The Boeing Company. Invention is credited to Rodney E. Bahr, Douglas A. McCarville.
United States Patent |
5,919,543 |
McCarville , et al. |
July 6, 1999 |
Composite sine wave spar
Abstract
A method of forming composite sine wave spars from composite
material. In accordance with the method, the sine wave spar is
formed of web plies, filler plies, separator plies and cap plies.
The edges of the web plies are cut to form a plurality of teeth
having different geometric configurations. The web plies are first
formed to the sine wave contours of a tool having the desired final
part geometry. The teeth of the web plies are then folded over the
edges of the tool to form a portion of the flanges of upper and
lower U-shaped channels. The portions of the flanges of the
U-shaped channels not covered by the teeth are formed using filler
plies that intermesh with the teeth to form a layer of the flanges
of the respective upper or lower U-shaped channel. The flanges are
reinforced through the use of separator plies that are placed
between the filler plies. The formed upper and lower U-shaped
channels are joined together so that their respective flanges are
located in line with each other. The triangular recesses between
the flanges of the joined upper and lower U-shaped channels are
filled with radius fillers having a triangular cross-section. Once
the radius fillers are in place, cap plies are placed over the
radius fillers and flanges to further reinforce the flanges. In the
preferred embodiment, each web ply has eight different teeth
configurations. The teeth are configured to fold over the edges of
the sine wave contour and cover the edges of the sine wave contour
in order to minimize overlapping and gaps between the folded over
teeth.
Inventors: |
McCarville; Douglas A. (Auburn,
WA), Bahr; Rodney E. (Wichita, KS) |
Assignee: |
The Boeing Company (Seattle,
WA)
|
Family
ID: |
24362909 |
Appl.
No.: |
08/912,159 |
Filed: |
August 15, 1997 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
|
590606 |
Jan 24, 1996 |
5843355 |
|
|
|
Current U.S.
Class: |
428/112; 428/119;
428/114; 264/258; 156/216; 156/182; 264/152 |
Current CPC
Class: |
B64C
1/065 (20130101); B29C 70/345 (20130101); B29D
99/0007 (20130101); B29D 99/0005 (20210501); B29C
70/543 (20130101); B64C 2001/0072 (20130101); Y10T
428/24174 (20150115); B29L 2031/7736 (20130101); Y10T
156/1003 (20150115); Y10T 428/24116 (20150115); Y10T
428/24132 (20150115); Y10T 156/1028 (20150115); Y10T
156/1034 (20150115); B29L 2031/3076 (20130101); Y02T
50/40 (20130101) |
Current International
Class: |
B29C
70/04 (20060101); B29C 70/54 (20060101); B29C
70/34 (20060101); B29D 31/00 (20060101); B64C
1/00 (20060101); B64C 1/06 (20060101); B32B
003/04 () |
Field of
Search: |
;264/257,258,160,152
;156/153,148,182,197,212,216 ;428/112,114,119,178,182,184 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Primary Examiner: Vargot; Mathieu D.
Attorney, Agent or Firm: Hammar; John C.
Parent Case Text
REFERENCE TO RELATED APPLICATIONS
The present application is a divisional application based upon U.S.
patent application 08/590,606, filed Jan. 24, 1996, now U.S. Pat.
No. 5,843,355.
Claims
The embodiments of the invention in which an exclusive property or
privilege is claimed are defined as follows:
1. A thermoplastic composite sine wave spar for use in an aerospace
structure formed by:
(a) cutting a plurality of individual layers of thermoplastic
composite prepreg material to define at least one web ply and at
least one cap ply;
(b) cutting at least one edge of the web ply to form a plurality of
teeth along the edge;
(c) positioning the web ply on a forming surface of a tool, the
forming surface having a sine wave contour complementary with the
desired shape of a web of the spar;
(d) folding the teeth on the web ply over over at least one edge of
the forming surface to form a flange extending from the web;
(e) placing the cap ply over the flange to form a laminated cap;
and
(f) consolidating the web ply and the laminated cap to produce the
formed sine wave structure.
2. A laminated, composite sine wave spar having a sine wave web
that extends between integral, opposing flanges, made by:
(a) cutting individual layers of a composite prepreg material
containing a resin carried on fiber reinforcement to define a
plurality of web plies, a plurality of filler plies, and a
plurality of cap plies, the plies being adapted for being laminated
together to define the sine wave spar upon consolidation of the
resin;
(b) cutting each web ply to form teeth along opposed edges;
(c) placing the web plies over one another to form a web laminate
on a sine wave contoured forming surface of a first tool;
(d) placing a corresponding, matched tool over the web laminate to
enclose the web plies while leaving the teeth of the web plies
exposed from edges of the first tool and matched tool;
(e) folding the teeth on each of the web plies over the edges along
the forming surface of the first tool or the matched tool the
folded teeth defining an integral flange on both edges for the web
laminate;
(f) placing at least one filler ply adjacent to the teeth of each
flange, one filler ply being placed for each layer of web ply in
the flange, each filler ply having an edge of teeth complementary
with the tooth edge of the adjacent web ply;
(g) placing the cap plies over the flange to form a sine wave spar;
and
(h) consolidating the resin in the sine wave spar by applying heat
and pressure to produce a composite.
3. The spar of claim 2, wherein the spar is made by the method
further comprising the steps of:
(a) providing tools having matched, U-shaped forming surfaces that
include a sine wave contour; and
(b) forming the teeth on the web plies over opposing edges of the
U-shaped forming surfaces to form the integral, opposing flanges,
thereby forming U-shaped channels each having a central sine wave
web.
4. The spar of claim 1, wherein the thermoplastic composite prepreg
material is PEEK, PEKK, or polyimide.
5. The spar of claim 1 wherein the prepreg material is carbon-fiber
reinforced polyimide.
6. The spar of claim 4 wherein the prepreg material is a
unidirectional tape.
7. The spar of claim 3 wherein the method of making the spar
further comprises the steps of:
(a) forming a radius filler from strips of the composite prepreg
material; and
(b) placing the radius filler into a triangular gap created between
the flanges of the joined U-shaped channels between the flange and
the cap plies.
8. The spar of claim 2 wherein the teeth are shaped to minimize
either overlapping plies of the web plies and the filler plies or
gaps between the adjacent web plies and the filler plies when the
teeth are folded.
9. A sine wave spar having integral flanges, comprising:
(a) a web contoured with a sine wave along a longitudinal direction
and integral flanges on opposed edges, the web including a
plurality of plies laminated together, each ply including a tooth
pattern cut along each edge, each web ply folded to define a web
and opposed flanges on each edge;
(b) filler plies in the flanges having an edge cut complementary
with the tooth pattern of an adjacent web ply adapted to minimize
overlapping or gaps;
(c) at least one cap ply overlying each flange; and
(d) a radius filler between the web plies and the cap ply; wherein
the web plies, filler plies, and cap plies contain resin
impregnated fiber reinforcement.
10. The spar of claim 9 wherein the plies are unidirectional
tape.
11. The spar of claim 9 wherein the resin is PEEK, PEKK, or
polyimide.
12. The spar of claim 9 wherein the resin is a thermoplastic.
Description
FIELD OF THE INVENTION
The present invention relates to a composite sine wave spar.
BACKGROUND OF THE INVENTION
The use of composite materials in the manufacture of aircraft and
other lightweight structures has increased steadily since the
introduction of such materials. Composite materials have a high
strength-to-weight ratio and high stiffness, making them attractive
for use in lightweight aircraft structures. Some drawbacks to using
composite materials have been high fabrication costs and low damage
tolerance. Generally, it has been difficult to produce parts formed
of high-strength composite materials at the same cost as comparable
metal parts. It has also generally not been possible to produce
composite parts having the same degree of damage tolerance as
comparable metal parts. These cost and damage tolerance differences
between composite and metal parts are especially notable in large
scale parts having complex contours.
Another disadvantage of composite materials has been their
relatively low temperature tolerance. The introduction of
thermoplastic composite materials has increased the temperature
tolerance of composites. In addition to having higher temperature
tolerance, thermoplastic composites are impervious to most
chemicals and have superior strength in some applications making
them ideal candidate materials for advanced aircraft. However,
manufacturing difficulties have generally made it difficult, if not
impossible, to fabricate complex parts from such thermoplastic
composite materials.
One of the contributors to such fabrication difficulty has been the
form in which most thermoplastic composite materials are obtained
from a material supplier. Generally, thermoplastic composite
materials come in rolls of flat material having unidirectional
reinforcement fibers embedded within a stiff, polymerized plastic
matrix. Such rolls are currently available in widths ranging from
approximately a 1/4 inch to a foot. The thermoplastic matrix
material is in a solid state, thus resulting in a slick, flat,
nonformable material. The stiffness of the thermoplastic composite
material prevents it from being easily bent or formed around
complex contours. In addition, even if formed around a contour, the
thermoplastic material maintains a memory such that once the
forming pressure is released the material returns to its flat
shape.
The stiff, nondeformable nature of most prior thermoplastic
composite materials have relegated them to use in simple parts
having gentle contours such as flat panels, fuselage doors, etc. It
would be advantageous if thermoplastic composite materials could be
used in highly stressed primary aircraft structure such as ribs and
spars. In the past, the complex contours of most aircraft's primary
structure has prevented thermoplastic composite materials from
being used. Due to the stiff, nondeformable nature of the
thermoplastic composite materials, it has generally not been
possible or cost-effective to produce high-quality parts having
such complex contours. One of the primary aircraft structures that
could be advantageously formed from thermoplastic composite
materials is sine wave spars for aircraft wing structures.
Aircraft spars can be formed of C-channels, I-beams, or I-beams
having sine wave central webs. Sine wave spar configurations have
been found to provide superior weight and strength properties in
most aircraft structures when compared to other spar shapes. In
order to form sine wave spars of thermoplastic composite materials,
the thermoplastic composite materials must be formed around complex
sine wave contours and sharp radius corners in order to form the
web and caps of the spar. Prior art manufacturing techniques have
not been able to produce high-quality formed sine wave spars from
thermoplastic composite materials.
One method tried to overcome fabrication difficulties with
thermoplastic materials is the use of a cloth composite material
having a thermoplastic matrix material that is applied to the
reinforcing fibers in a powder form. During processing, the
thermoplastic matrix material is heated to a temperature at which
the matrix material flows together to form a consolidated
thermoplastic composite part. However, such cloth materials are
expensive, and have been prone to problems associated with fiber
wet-out, voids, etc. In addition, the use of cloth materials is not
as structurally efficient as the use of unidirectional composite
materials.
As can be seen from the discussion above, there exists a need for
methods and apparatus to form thermoplastic composite materials
into complex shapes such as sine wave spars for use in aircraft
applications. The present invention is directed toward meeting this
need.
SUMMARY OF THE INVENTION
The present invention allows sine wave spar structures to be
produced using unidirectional thermoplastic or other composite
prepreg material while reducing the occurrence of wrinkles, folds,
etc. in the individual layers of the formed sine wave spar
structure.
In accordance with one embodiment of the present invention, a sine
wave structure having a sine wave web and at least one flange
extending outward from the web is formed of a thermoplastic
composite material. Individual layers of thermoplastic composite
prepreg material are first cut to form web plies and cap plies. The
web plies are then cut to form a plurality of teeth that extend
outward from at least one edge of each ply. The cut web plies are
placed on and formed to the forming surface of a tool having a sine
wave forming surface. After deforming the web plies to the contour
of the forming surface, the teeth on the web plies are folded over
the edges of the forming surface in the region of the sine wave
contour to form one or more flanges. The cap plies are then placed
adjacent the flanges and the combination of cap plies and web plies
are consolidated to produce the formed sine wave spar
structure.
In accordance with other features of the invention, tools are
provided having U-shaped forming surfaces. The web plies are formed
over the U-shaped forming surfaces and the teeth are formed over
the edges of the U-shaped forming surfaces. The teeth are folded
over opposing edges of the U-shaped forming surface in the region
of the sine wave contour to form opposing flanges, thereby forming
a U-shaped channel having a central sine wave web.
In accordance with other aspects of the invention, upper and lower
U-shaped channels are formed. Each U-shaped channel includes a
central web having a sine wave contour. The upper and lower
U-shaped channels are joined so that the central webs of the
channels are placed adjacent to each other so that the flanges of
the U-shaped channels are in line with each other.
In accordance with yet other aspects of the invention, a triangular
shaped radius filler having a sine wave contour is formed from
strips of the thermoplastic composite prepreg material. The radius
fillers are placed into triangular gaps created between the flanges
of the joined upper and lower U-shaped channels.
In accordance with still other aspects of the invention, filler
plies are cut from the thermoplastic composite prepreg material.
The filler plies include one or more recesses along one edge. The
filler plies are placed adjacent the folded over teeth of the web
plies so that one or more of the teeth extend into the recesses in
the filler plies. Separator plies are also cut from the
thermoplastic composite prepreg material. One edge of the separator
plies are cut to form a sine wave contour. The separator plies are
placed over the folded over teeth and filler plies in order to form
a layer of the flanges of the U-shaped channel.
In accordance with yet other aspects of the invention, the
dimensions of the teeth on the web plies are determined in order to
reduce the formation of gaps between the edges of the teeth after
the teeth are folded over the edges of the forming surface. The
shape and dimensions of the teeth are also determined to prevent
the teeth from overlapping one another after the teeth are folded
over the edges of the forming surface. In one embodiment, a
plurality of teeth having approximately the same size and shape are
used. In other embodiments, the web plies are cut to form at least
three different shapes of teeth or at least eight different shapes
of teeth.
In accordance with still further aspects of the invention, the
teeth of the web ply are folded over the edges of the forming
surface in the region of the sine wave contour using a hot
iron.
In other embodiments of the invention, the sine wave spar structure
may be formed from unidirectional thermoplastic composite prepreg
material including PEAK, HTA, K-IIIB, PEKK, Radel-X or Ultem.
The present invention allows sine wave composite I-beam spars to be
formed of stiff thermoplastic composite prepreg. The invention's
use of web plies having a plurality of teeth allows the web plies
to be folded around the edges of a sine wave spar tool without
creating excessive wrinkling. Folding the teeth around the edges of
the sine wave spar also increases the structural strength between
the web of the sine wave spar and the caps of the sine wave spar.
High web to cap strengths are particularly important in highly
loaded aircraft sine wave spars.
BRIEF DESCRIPTION OF THE DRAWINGS
The foregoing aspects and many of the attendant advantages of this
invention will become more readily appreciated as the same becomes
better understood by reference to the following detailed
description, when taken in conjunction with the accompanying
drawings, wherein:
FIG. 1 is a top view of a thermoplastic composite sine wave spar
formed in accordance with the present invention;
FIG. 2 is a side elevational view of the sine wave spar of FIG.
1;
FIG. 3 is an end view of the sine wave spar of FIG. 1;
FIG. 4 is an exploded view showing a portion of the individual
composite subassemblies that form the composite sine wave spar;
FIG. 5 is a partially exploded view showing the assembly of the
upper and lower C-channels;
FIG. 6 is a partially exploded view of the upper and lower
C-channels, radius fillers, and cap plies;
FIG. 7 is a cross-section showing a portion of a ply configuration
for one embodiment of a sine wave spar formed in accordance with
the present invention;
FIG. 8 is a perspective view of one embodiment of the forming of a
portion of a web ply around a sine wave contour;
FIG. 9 is a perspective view of another embodiment of the forming
of a portion of a web ply around a sine wave contour;
FIG. 10 is a side elevational view showing the preferred embodiment
of the forming of a portion of a web ply around a sine wave
contour;
FIG. 11 is a top view illustrating one embodiment of a web ply, cap
filler ply, cap separator ply, and cap ply;
FIG. 12 is an enlarged view of a portion of the web ply of FIG.
11;
FIG. 13 is an enlarged view of a portion of the separator ply of
FIG. 11;
FIG. 14 is a cross-section of a portion of the preferred ply
configuration according to the invention;
FIG. 15 is a perspective view of the radius filler tooling and
radius filler workpiece;
FIG. 16 is an end view of the radius filler tooling in an open
position;
FIG. 17 is an end view of the radius filler tooling in a closed
position;
FIG. 18 is an end view of the preferred embodiment of the sine wave
spar tooling;
FIG. 19 is an exploded view of the lower tooling;
FIG. 20 is a perspective view of the assembled lower tooling;
FIG. 21 is a partially exploded view of the sine wave spar
tooling;
FIG. 22 is another partially exploded view of the sine wave spar
tooling; and
FIG. 23 is a graph of elapsed time versus part temperature wherein
elapsed time is plotted along the x-axis and part temperature is
plotted along the y-axis.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
The present invention is a method and apparatus to form composite
parts from prepreg composite materials. The invention is described
below with respect to a preferred embodiment used to form a sine
wave spar 30 from an unidirectional thermoplastic composite
material. However, the method and apparatus of the invention may be
used to form a variety of composite structures. Similarly, the
present invention may be used to form composite parts out of
various composite materials including fiber reinforced epoxy matrix
composite prepreg, bismaleimide matrix composite prepreg, or
thermoplastic matrix composite materials such as K-IIIB, PEEK, HTA,
PEKK, Radel-X or Ultem, etc. The composite prepreg used can be
reinforced with unidirectional fibers, such as fiberglass,
graphite, or Kevlar.RTM. fibers. The use of unidirectional
composite prepreg can also be combined with the use of cloth
prepreg composite materials to form the composite part.
FIG. 1 illustrates a sine wave spar 30 fabricated according to a
method of the present invention as described below. As best
illustrated in FIGS. 1-3, the sine wave spar 30 is generally an
I-beam having a central sine wave web 32 that extends between
opposing spar caps 34 and 36, respectively. The spar caps 34 and 36
are inclined at an angle with respect to the sine wave web 32 such
that the leading edges 31 of the caps are closer together than the
trailing edges 33 (FIG. 3).
For clarity, an overview of the method of forming the composite
sine wave spar 30 will first be discussed below. The individual
forming steps and associated tooling etc., will then be discussed
in more detail.
In the preferred embodiment, the sine wave spar 30 is fabricated
using several preformed composite subassemblies that are joined
together in an assembly process to form an unconsolidated formed
composite workpiece 38 (FIG. 6). The formed composite workpiece 38
is then placed within a sine wave tooling concept 40 (FIG. 18). The
workpiece 38 and tooling concept 40 are then vacuum bagged and
placed within an autoclave (not shown) where the composite
workpiece is formed under a vacuum and a high pressure
consolidation force at an elevated temperature.
Although the preferred embodiment of the invention is described
below with respect to the use of an autoclave, the invention could
be used with other fabrication equipment. For example, the present
invention could be used along with a heated forming press or within
a forming press using tools having an integrated heat source such
as cal rods, induction heaters, etc.
As discussed in the background section, unidirectional
thermoplastic composite materials are generally available as rolls
of prepreg having a maximum width of approximately one foot.
Therefore, in order to form larger parts, the relatively narrow
one-foot wide prepreg materials are first seamed together to form
wider sheets of material. Once seamed, the sheets of composite
prepreg material are cut to the desired dimensions using a water
jet cutter, Gerber cutter, or other appropriate cutting device.
These individual cut-out layers or plies of thermoplastic composite
material are then formed to the desired shapes and tacked together
or, in some instances, preconsolidated to form the subassemblies
that are used to form the composite workpiece 38 as described
below.
In the preferred embodiment, the composite workpiece 38 is
assembled from preformed composite subassemblies including lower
and upper U-shaped channels 42 and 44 (a portion of which is shown
in FIG. 4), left and right radius fillers 46 and 48, and left and
right caps 50 and 52. The lower and upper U-shaped channels 42 and
44 are formed by laying the cut out individual layers of
unidirectional composite prepreg over the sine wave forming
surfaces 55 and 57 of lower and upper tools 54 and 56, respectively
(FIGS. 20 and 21), and then tacking or taping them together, as
described in detail below.
The left and right caps 50 and 52 are formed by laying cut out
individual layers of unidirectional composite prepreg material over
the forming surfaces 59 and 61 of left and right cap tools 58 and
60, respectively (FIGS. 18 and 21). The laid-up left and right caps
50 and 52 are then tacked together and preconsolidated in order to
simplify the assembly of the composite workpiece 38, as described
below.
The left and right radius fillers 46 and 48 are formed of
individual strips of thermoplastic composite prepreg that are
stacked side-by-side to form a blank 140 as illustrated in FIGS. 15
and 16. The blank 140 is placed within the forming cavity 142 of a
radius filler tool 62. The blank 140 is then preconsolidated into a
sine wave shape using the radius filler tool 62 as described in
more detail below. After consolidation, the left and right radius
fillers 46 and 48 have the correct sine wave shape to fit between
the assembled lower and upper U-channels 42 and 44 (FIG. 5), as
described below.
After the lower and upper U-shaped channels 42 and 44 are
fabricated out of individual layers of prepreg, they are placed
together as illustrated in FIG. 5. The lower and upper U-shaped
channels 42 and 44 are placed together so that the sine wave
contours of the channels fit together and so that the flanges 63
(FIG. 5) on the lower U-shaped channel 42 are aligned with the
flanges 65 on the upper U-shaped channel as illustrated in FIG. 6.
Once assembled, the lower and upper U-shaped channels 42 and 44 may
either be held together by clamps or tape or may be tacked together
using a heat iron, heat gun, etc. Due to the rounded edges on the
corners of the lower and upper U-shaped channels 42 and 44, a
triangular gap 134 (FIG. 14) is formed along both edges of the
intersection between the joined surfaces of the U-shaped
channels.
The triangular gaps 134 are filled using the left and right radius
fillers 46 and 48. The radius fillers 46 and 48 are placed in the
triangular gaps 134 and tacked in place using a heat gun, hot iron,
tape, etc., as illustrated in FIG. 6. After the radius fillers 46
and 48 are in place, the preconsolidated left and right caps 50 and
52 are placed in contact with the joined flanges 63 and 65 of the
U-shaped channels 42 and 44 as best seen in FIG. 6, thus forming
the composite workpiece 38 FIG. 18).
The formed composite workpiece 38 is then placed within the tooling
concept 40 and consolidated. The preferred embodiment of the
tooling concept 40 includes upper tools 56, lower tools 54, and
left and right cap tools 58 and 60, as illustrated in FIG. 18. As
described in more detail below, in order to avoid trapping the
tools within the formed composite sine wave spar 30, the lower
tools 54 are formed of three pieces namely, a left tool 150, a
right tool 152, and a center tool 154. Similarly, the upper tools
56 are formed of a left tool 156, a right tool 158 and a center
tool 160.
The upper and lower tools 56 and 54 and left and right cap tools 58
and 60 fit together around the composite workpiece 38 in order to
define the part geometry of the formed sine wave spar 30 as
described in more detail below. The combined assembly comprising
the composite workpiece 38 and tooling concept 40 is placed within
a vacuum-bag (not shown) and then placed within an autoclave and
processed.
The interior of the vacuum bag is connected to the autoclave's
vacuum exhaust (not shown) in order to remove any air within the
vacuum bag and any volatiles produced during consolidation of the
composite workpiece 38. During processing, the autoclave is
pressurized to apply an inwardly directed force on the tooling
concept 40 as illustrated by arrows 66 in FIG. 18. This inward
directed force places a consolidation pressure on the various
surfaces of the composite workpiece 38. At the same time, the
tooling concept 40 and composite workpiece 38 are heated in
accordance with the processing requirements of the composite
material used. The combination of the elevated temperature and
consolidation force applied to the composite workpiece 38
consolidates and forms the composite workpiece to the interior
dimensions of the tooling concept 40, thus producing a formed
composite sine wave spar 30.
In the preferred embodiment, the sine wave spar 30 is formed of
HTA/IM8 thermoplastic composite material. For this material, the
processing cycle shown in FIG. 23 was used to produce a high
quality formed composite part. The composite tooling concept 40 and
composite workpiece 38 were heated to 710.degree. F. over
approximately 480 minutes. During the heating of the tooling
concept and composite workpiece, a 10-15 psi vacuum was applied to
the interior of the vacuum bag and held during processing. When the
temperature of the composite workpiece 38 reached approximately
650.degree. F. in approximately 300 minutes, a consolidation
pressure of 200 psi was applied and held until the composite
workpiece reached the 100.degree. F. temperature. After
consolidation, the temperature of the composite workpiece 38 was
reduced and the formed composite part was removed at approximately
700.degree. F.
The processing parameters illustrated in FIG. 23 produced a high
quality part using the material system identified for the preferred
embodiment. However, other composite material systems could require
different processing parameters in order to produce the best
quality part. A range of processing parameters capable of producing
high quality parts is generally provided by the supplier of the
material used. In addition to the material selected, the
thicknesses of the composite workpiece 38 and the thermal mass of
the composite tooling concept 40 also affect the optimization of
the processing parameters.
The process by which the individual subassemblies used to form the
composite workpiece 38 are formed will now be described in more
detail. As discussed in the background section, one of the
difficulties in forming parts from unidirectional thermoplastic
composite materials is their stiff, cardboard-like nature that
prevents them from being easily formed around complex contours.
Thus, although thermoplastic composite materials have been
successfully used to form simple structures such as U-shaped
I-beams, curved wing or fuselage panels, etc., they have not
generally been successfully used to form more complex structures
such as aircraft sine wave spars.
One of the difficulties in fabricating the composite sine wave spar
30 is to form the individual layers of thermoplastic composite
prepreg around the sine wave spar tools without creating puckering,
wrinkling, etc. Another difficulty is to form individual layers of
thermoplastic composite around the sine wave spar tooling so that
the individual layers maintain their shape so that additional
layers may be formed over the top of the formed layers.
In order to form sine wave spars out of thermoplastic composite
materials, the layers of composite material are formed around
complex sine wave contours. In the invention, a lay-up
configuration is used that allows the individual layers of
thermoplastic composite material to be formed around complex sine
wave contours without creating undesirable wrinkles in the
composite material. During development of the preferred lay-up
configuration, different ply configurations were developed and used
with varying degrees of success.
A first embodiment of a ply configuration used to form the sine
wave spar 30 is illustrated in FIGS. 7 and 8. In the first
embodiment, several layers of prepreg composite material are used
to form the web 32 of the sine wave spar 30 and additional layers
of prepreg composite material are used to form the caps 34 and 36
of the composite sine wave spar. In order to obtain sufficient
strength to carry loads from the web 32 into the caps 34 and 36,
each layer of prepreg composite material used to form the web 32 is
folded through a 90.degree. bend 70 (FIG. 7). This allows the outer
portion 71 of each layer of composite material forming the web 32
to form a flange 73 lying adjacent to the interior surface of the
respective cap 34 or 36. Thus, in the preferred embodiment, the
lower and upper U-shaped channels 42 and 44 are formed so that they
include the respective flanges 63 and 65.
For ease of description, the fabrication of only a portion of a
representative lower or upper U-shaped channels 42 or 44 is
described below. The fabrication is described with respect to a
representative forming tool 72 that has a representative sine wave
forming surface. In actual application, the individual layers of
composite material forming the lower and upper U-shaped channels 42
and 44 are formed over the forming surfaces 59 and 61 (FIGS. 20 and
21) of the lower and upper forming tools 54 and 56,
respectively.
As illustrated in FIG. 8, in order to form the flanges 73, each
layer of prepreg composite material forming the web 32 is formed
over the forming surface of the forming tool 72. The individual
layers of composite material 68 are first pressed downward as
illustrated by arrow 69 so that the layer of material conforms to
the sine wave contour. The edges of each layer 68 are then folded
over the edges of the tools 72 as described below.
In the first configuration shown in FIG. 8, the edges of each layer
68 of prepreg composite are slit at equally spaced intervals and to
the same depth in order to form rectangular tabs or teeth 74. The
teeth 74 are formed by slitting the prepreg composite material
perpendicularly to the edges of the material as shown in FIG. 8.
The slits allow each of the teeth 74 to be individually folded over
the edge of the tool 72. Due to the stiff nature of the prepreg
composite, each of the teeth 74 are folded over by locally heating
the layer 68 of prepreg composite material to an elevated
temperature at which the viscosity of the material allows the
material to be bent over the edges of the tool 72. In the preferred
embodiment, the teeth 74 are folded over using a hot iron operating
at approximately the melting temperature of the thermal plastic
matrix in the composite material.
As illustrated in FIG. 8, in the first configuration, the teeth 74
are formed of equal sizes and lengths. The slits along the edges of
the layer 68 of composite prepreg allow the teeth 74 and thus layer
of prepreg to be conformed to the sine wave contour of the tool 72.
However, because the teeth 74 are similarly sized, the teeth
overlap at the peaks 76 of the sine wave contour and leave gaps
(not shown) between the individual teeth in the valleys 78 of the
sine wave contour.
After each layer 68 of prepreg used to form the web 32 is applied
to the tool 72 and formed around the edges of the tool, the layers
are joined together to form the upper or lower U-shaped channels as
shown in FIGS. 5 and 6. The U-shaped channels 42 and 44 are joined
by tacking the individual layers of prepreg together using a hot
iron or by taping them together. If tacking is used, a hot iron is
briefly placed on the composite material at spaced intervals over
the length and width of the layers of composite material. The hot
iron locally heats and melts the matrix material in the layers of
composite material, thus locally joining them together.
After the U-shaped channels 42 and 44 are joined together, the
radius fillers 46 and 48 are placed in the triangular gaps 134
between the channels. The preconsolidated caps 50 and 52 are then
placed adjacent the flanges formed by the folded-over teeth 74 of
the web plies as described above and as shown in FIG. 7. The
resulting composite workpiece 38 is then placed within the tooling
concept 40, vacuum bagged and cured as discussed above to produce
the sine wave spar 30.
The first ply configuration produced a void-free, reasonable
quality sine wave spar that was aesthetically acceptable. Upon
testing the resulting sine wave spar 30, it was found that there
was insufficient strength between the web 32 and the caps 34 and 36
for application to highly stressed aircraft spars requiring high
strength between the web and the caps. However, the sine wave spar
30 produced using the first ply configuration can be used for other
applications in which the strength between the web 32 and caps 34
and 36 need not be as high.
Using the information learned from the first ply configuration
illustrated in FIG. 8, a second ply configuration was created as
illustrated in FIG. 9. The same general idea used in the first ply
configuration was carried over to the second ply configuration,
i.e., the edges of each layer 68 of composite material used to form
the web 32 were slit to form teeth that can be folded over the
edges of the sine wave contour of the tool 72. However, in the
second ply configuration the teeth were not maintained at a
constant size or shape. As illustrated in FIG. 9, the edges of each
layer of thermoplastic composite material 68 were cut to form four
different teeth configurations. The portion of each layer of
composite material located in the valleys 78 is slit perpendicular
to the edge of the material to form three equally sized rectangular
teeth 80. The portions of the composite material placed along the
relatively flat sides 82 of the sine wave contour is slit
perpendicular to the edge of the material to form larger left and
right teeth 84 and 86 respectively. The outer edges of each of the
teeth 84 and 86 are cut at a slant so that the edge of each tooth
closest to a tooth 80 is longer than the opposite edge of the
respective tooth. The portion of the composite material 68 located
at the peaks 76 of the sine wave contour is slit at an angle to
form four triangular teeth 88. The triangular teeth 88 are tapered
to a point at their outermost edge.
After slitting the edges of the composite material 68 to form the
teeth 80, 84, 86 and 88, the composite material is pressed into the
sine wave contour of the tool 72 as shown in FIG. 9. The teeth 80,
84, 86 and 88 are then folded over the edges of the sine wave
contour using a heat iron as described above. The rectangular teeth
80 fold over the edge of the sine wave contour in the region of the
valley 78. After the rectangular teeth 80 are folded over, a
triangular gap 89 is left between the edges of each of the
rectangular teeth 80. The larger teeth 84 and 86 fold over so that
they extend downward and inward from the sides 82 (FIG. 9). The
length of the teeth 84 and 86 and the angle at which the outer
edges of the teeth 84 and 86 are cut is determined so that the
outer edges of the teeth 84 and 86 lie adjacent each other once the
teeth 84 and 86 are folded over. The teeth 88 are cut at angles so
that the edges of one of the teeth 88 lie adjacent the edges of the
adjoining teeth once the teeth are folded over the sine wave
contour in the region of the peak 76.
In a manner similar to that described above with respect to the
first ply configuration, after each individual layer of composite
material is placed and conformed to the sine wave contours of the
tools they are tacked together to form the upper and lower U-shaped
channels 42 and 44. The channels 42 and 44 are then joined as
described above. The radius fillers 44 and 48 are then placed in
the triangular gaps 134 between the joined U-shaped channels and
the caps 50 and 52 are applied to form the composite workpiece 38.
The composite workpiece 38 is then placed within the tooling
concept 40 and cured according to the processing parameters of the
material as described above.
The second ply configuration produced a high quality thermoplastic
composite sine wave spar 30 relatively free of voids etc. The
second ply configuration also resulted in improved strength between
the web 32 and caps 34 and 36 of the sine wave spar. This increased
strength is primarily due to the increased size of the flanges
produced using the second ply configuration. However, the second
ply configuration still lacked sufficient strength between the web
32 and caps 34 and 36 of the resulting sine wave spar for highly
loaded aircraft configurations. In addition, the second ply
configuration created fiber directional discontinuities and
inefficiencies in the resulting sine wave spar. When a layer of
composite material having reinforcing fibers oriented at either
plus or minus 45.degree. is used in the second ply configuration,
the fiber orientation in the location of the left and right teeth
84 and 86 became 0.degree. and 90.degree.. The different fiber
orientations in the left and right teeth 84 and 86 changes the
strength and stiffness of the layer of composite material in the
area of the left and right teeth 84 and 86. Thus, the second ply
configuration results in load discontinuities in the area of the
left and right teeth 84 and 86 due to the changing fiber
orientations.
The lessons learned from the first and second ply configurations
were used to create the preferred ply configuration illustrated in
FIGS. 10-14. In the preferred ply configuration, one of the goals
was to improve the peel strength between the web 32 of the sine
wave spar 30 and the caps 34 and 36 of the sine wave spar. Another
goal was to minimize any load discontinuities by maintaining
consistent fiber orientation wherever possible.
In the preferred ply configuration, the sine wave spar 30 is formed
using four different basic ply configurations, i.e., web plies 118
(FIG. 11), filler plies 120, separator plies 128, and cap plies
132. The web plies 118 are used to form the web 32 of the sine wave
spar and to fold over around the edges of the tooling to form part
of the caps 34 and 36. The filler plies 120 are configured to
intermesh with the folded over portions of the web plies 118 to
form a continuous layer of composite material throughout the caps
34 and 36. The separator plies 128 are placed between selected
layers of filler plies 120 in order to further reinforce the caps
32 and 34. The cap plies 132 are placed on the exterior of the
partially formed caps 34 and 36 and extend the width and length of
the caps to provide additional reinforcement. The configuration and
use of the web plies 118, filler plies 120, separator plies 128 and
cap plies 132 are discussed in more detail below.
First, the upper and lower U-shaped channels 42 and 44 (FIG. 4) are
formed using the web plies 118, filler plies 120 and separator
plies 128. The individual U-shaped channels 42 and 44 are formed by
first pressing and forming individual web plies 118 to the sine
wave contour of the respective upper or lower tools 54 or 56. An
example of the forming process is shown on the exemplary tool 72 in
FIG. 10. The teeth (discussed in more detail below) extending from
the edges of each web ply 118 are folded over the edges of the tool
to form a portion of the flanges on the respective U-shaped channel
42 or 44 (FIG. 19). A filler ply 120 is then placed in contact with
the folded over teeth forming a portion of the flanges to extend
the individual layer of composite material so that a single layer
of composite material extends over the web 32 and around the edges
of the tool to form one layer of the flange as best seen in FIGS.
10 and 14. Periodically, separator plies 128 are placed over the
folded over teeth of the web plies 118 and over the filler plies
120 to reinforce the flanges of upper or lower channels 42 or
44.
After all of the web plies 118, filler plies 120 and separator
plies 128 are in place, they are tacked together or taped together
to form the respective left and right U-shaped channels 42 and 44.
The lower and upper U-shaped channels 42 and 44 are then placed
together and the left and right radius fillers 46 and 48 (FIG. 6)
are put in place. The preconsolidated cap plies 132 are then placed
over the top of the flanges formed by the left and right U-shaped
channels in order to reinforce and complete the caps as described
above.
In the preferred embodiment, the edges of each web ply 118 are cut
to form six different configurations of teeth as best illustrated
in FIGS. 10 and 12. Starting at the location on the web plies 118
that is to be placed in the center of the valley 78 (FIG. 10) of
the sine wave contour, a rectangular tooth 90 is formed. Each
rectangular tooth 90 is formed by making two parallel cuts
perpendicular to the edges of the web ply 118. When placed on the
tool 72 and folded over the edge of the tool, the rectangular tooth
90 extends perpendicular to the edge 113 (FIG. 10) of the flanges
of the respective U-shaped channel being formed. Each tooth 90 is
cut to a prespecified length so that it extends only partially
across the width of the flange as described in more detail
below.
The composite material to the left and right of each rectangular
tooth 90 is cut to form left and right trapezoidal teeth 92 and 94
as best seen in FIG. 12. The left and right trapezoidal teeth 92
and 94 are reflections of each other around the centerline of the
rectangular tooth 90. The edges of the right and left teeth 92 and
94 furthest away from the rectangular tooth 90 extend perpendicular
to the edge of the web ply 118. The outer edges 98 of the teeth 92
and 94 slope inward from the edges of the teeth furthest from the
rectangular tooth 90 toward the rectangular tooth 90 as illustrated
in FIG. 12. The angle at which the outer edges 94 of the teeth
slope is determined so that the outer edges extend parallel to the
outer edge 113 (FIG. 10) of the flange once the left and right
trapezoidal teeth 92 and 94 are folded over the edges of the tool
72.
An elongated trapezoidal tooth 102 is formed to the left of each
left tooth 92. The length of each trapezoidal tooth 102 is sized so
that it extends approximately over the length of the sides 82 (FIG.
10) of the sine wave contour once folded over the edges of the tool
72. The opposing edges of the trapezoidal tooth 102 are formed by
cutting the web ply 118 perpendicular to its edges as illustrated
in FIG. 12. The outer edge 104 of the trapezoidal tooth 102 is cut
so that the edge of the trapezoidal tooth adjacent the left tooth
92 is longer than the opposite edge of the trapezoidal tooth thus
creating a slanted outer edge 104.
To the left of each trapezoidal tooth 102 is a left and a right
peak tooth 106 and 108 and a center peak tooth 110. The opposing
edges of the center peak tooth 110 slope inward from bottom to top
such that the width of the outer portion of the tooth is narrower
than the width of the inner portion of the tooth. The outer edge
111 (FIG. 12) of the center tooth 110 lies parallel to the edge 113
(FIG. 10 of the flange of the respective upper or lower U-shaped
channels once it is folded over the edge of the tool 72.) The left
and right 106 and 108 peak teeth are located to the left and right
respectively of the center tooth 110 and are mirror images of each
other about the centerline of the peak tooth 110. The edges of the
left and right peak teeth 106 and 108 closest to the center peak
tooth 110 slant away from the center tooth 110. The opposite edges
of the left and right peak teeth 106 and 108 slant inward and
downward so that once the left, right and center 106, 108 and 110
peak teeth are folded over the edge of the tool 72 in the location
of a peak 76, their edges fit together to cover the peak as
illustrated in FIG. 10.
A large fold-over tooth or flap 112 is located immediately to the
left of the left peak tooth 106. The tab 112 extends
perpendicularly outward from the edge of the web ply 118. The tab
112 then slants from left to right as illustrated in FIG. 13 (or
right to left as illustrated in FIG. 11 depending upon the edge of
the web ply). The width of the fold-over tab 12 is sized so that it
is approximately the same length as the side 82 (FIG. 10) of the
sine wave contour of the tool 72.
Once folded over the edge of the tool 72, the slanted edge 115
(FIG. 12) of the tab 112 extends parallel to the edge 113 of the
flange and is in line with the outer edges of the left and right
trapezoidal teeth 92 and 94 as best seen in FIG. 10. The end 119 of
the tab 112 is angled so that once the tab 112 and the trapezoidal
tooth 102 are folded over the opposing edges of a sine wave curve
in the tool 72, the edge 119 of the tab 112 lies adjacent the edge
104 of the tab 102.
As shown in FIG. 10, once the teeth of the web ply 118 are folded
over the edges of the sine wave contour of the tool 72, the teeth
106, 108 and 110 cover the peak 76 of the tool. The tab 112 and
trapezoidal teeth 104 cover the mid-section of each sine wave
contour and the left and right trapezoidal teeth 92 and 94 and
center teeth 90 cover the valley of the edge of the sine wave tool
72.
One goal of the preferred ply configuration is to have the various
teeth fit together to cover as much of the edge of the sine wave
tool as possible without leaving gaps (FIG. 10) between teeth. In
the preferred embodiment, the configuration of the teeth on the web
plies 118 leaves small triangular gaps 116 between the edges of the
trapezoidal teeth 102 and the left trapezoidal teeth 92 and the
edges of the right trapezoidal teeth 94 and the tabs 12. In
addition, small rectangular gaps 117 are left between the edges of
the left teeth 92 and the rectangular teeth 100 and the edges of
the rectangular teeth 100 and the right teeth 94.
As illustrated in FIG. 10, to form a constant thickness cap for the
sine wave spar 30 additional composite material is added in the cap
adjacent to the folded over teeth of the web plies 118 using the
filler plies 120. Each filler ply 120 (FIGS. 11, 12 and 15)
includes a plurality of rectangular cutouts 122 (FIG. 11). Each of
the cutouts 122 is sized and configured to allow each filler ply
120 to interlock with the folded over rectangular teeth 90 of each
web ply 118. As illustrated in FIG. 10, when in position, the
center teeth 90 fit into the recesses 122 in the filler ply 120 and
the inner edge 124 of the filler ply 120 contacts the edges 114,
and 98 of the tab 112 and teeth 92 and 94. The filler ply 120
completes each of the fold-over web plies 118 so that a continuous
layer of composite prepreg material extends along the surface of
the web 32, around the corner of the tool 72 and over the width of
the cap.
In the preferred embodiment, in order to add additional strength to
the caps a separator ply 128 is placed between every two filler
plies 120. As illustrated in FIG. 13, each of the separator plies
128 has a sine wave edge 130 that is contoured to follow the
contours of the sine wave surface of the respective upper and lower
U-shaped channels 44 and 42. Thus, once the separator ply 128 is in
place, it forms one layer of the respective flange of the lower and
upper U-shaped channel 42 or 44, as illustrated in FIG. 14.
Also as illustrated in FIG. 14 and as discussed above, the web
plies 118, filler plies 120 and separator plies 122 form the lower
and upper U-shaped channels 42 and 44. Once formed, the lower and
upper U-shaped channels 42 and 44 are placed together and joined as
described above. Once the lower and upper U-channels 42 and 44 are
joined, triangular gaps 134 (FIG. 14) are left between the flanges
of the channels. The gaps 134 are filled in order to prevent voids
and cavities in the formed composite part. As described above in
the preferred embodiment, the gaps 134 are filled using the
triangular radius fillers 46 and 48.
In the preferred embodiment, the radius fillers 46 and 48 are
formed by cutting individual strips or layers of unidirectional
composite prepreg lengthwise. These layers of unidirectional
composite prepreg are stacked together to form a blank 140 as
illustrated in FIG. 17. This blank 140 is then deformed and placed
within a forming cavity 142 in the bottom 141 of a radius filler
tool 62 (FIG. 16). The forming cavity 142 has a triangular
cross-section and a sine wave shape corresponding to that desired
for the formed radius fillers 46 and 48. The top 144 of the tool 62
is placed over the blank 140 and includes a male tool extension 145
that is sized to fit within the top of the forming cavity 142. Once
the blank 140 is inserted into the forming cavity 142 and the top
144 is in place, the tool is heated to an appropriate processing
temperature for the composite material used. The top and bottom
tools 141 and 144 are then pressed together so that the male
tooling extension 145 presses and forms the blank 140 to the
interior shape of the forming cavity 142. After forming, the formed
radius filler 46 or 48 is removed and placed within the gaps
134.
After the radius fillers 46 and 48 are placed within the gaps 134,
the preconsolidated cap plies 132 are placed over the radius
fillers and joined flanges of the lower and upper U-shaped channels
42 and 44. The resulting composite workpiece 38 is then placed
within the tooling concept 40 as described above.
Also as described above, in the preferred embodiment the sine wave
spar 30 has flanges that slope with respect to the central web 32.
In addition, in some embodiments, the sine wave spar 30 may curve
over its length (not illustrated). Therefore, in order to avoid
trapping either the upper or lower tools 56 or 54 within the formed
composite sine wave spar, the tools are formed of multiple pieces.
In the preferred embodiment, both the lower and upper tools 54 and
56 are formed of three separate pieces.
As illustrated in FIG. 19, the lower tools 54 include a left tool
150, a right tool 152, and a center tool 154. The left, right, and
center tools 150, 152, and 154 fit together as illustrated in FIG.
20 to form the lower tools 54. Each of the tools 150, 152, and 154
include upper forming surfaces that fit together to form the sine
wave forming surface 55 used to form one surface of the central web
32. In the preferred embodiment, the inner surface of the left and
right tools 150 and 152 are sloped inward as illustrated in FIG.
18. The center tool 154 has a wedge configuration that is wider at
the bottom of the tool than at the top. This allows the tools 150,
152, and 154 to fit together while allowing the center tool 154 to
be inserted or removed from between the left and right tools 150
and 152, both during assembly and disassembly of the tooling
concept 40. The left, right, and center tools 150, 152, and 154 all
include centrally located bores 164 (FIG. 18) that pass through the
width of the tools. The left, right, and center tools 150, 152 and
154 are maintained together after assembly by inserting tooling
rods 166 through the bores 164 after the tools are assembled.
The side tools 58 and 60 rest upon the top of the left and right
lower tools 150 and 152, respectively. As described above, the side
tools 58 and 60 include forming surfaces 59 and 61 that define the
exterior surface of the caps 50 and 52 (FIG. 18) after the
composite workpiece 38 is formed.
In the preferred embodiment, the lower tools 54 are first assembled
as shown in FIG. 20. The composite workpiece 38 is then placed on
the sine wave forming surface 55. The side tools 58 and 60 are then
placed on either side of the composite workpiece 38. The upper
tools 56 are then placed on top of the left and right side tools 58
and 60 as illustrated in FIGS. 18, 21 and 22.
The upper tools 56 include a left tool 156, a right tool 158, and a
center tool 160. The upper left, right, and center tools 156, 158,
and 160 fit together to form the upper forming surface 57 in a
manner similar to that described with respect to the lower tools
54. The inner edges of the left and right upper tools 156 and 158
slope inward and the center tool 160 has a wedge shaped
cross-section in a manner similar to that described with respect to
the lower tools 54. This allows the upper tools 56 to fit together
between the left and right side tools 58 and 60 as best seen in
FIGS. 18 and 22. The upper tools 56 also include bores 166 that
extend through the width of the tools. The upper tools 56 are held
together by tool rods 166 (FIG. 21) in a similar manner as
described above with respect to the lower tools 54.
Once the tooling concept 40 is assembled, the lower forming surface
55 defines the dimensions of the lower surface of the sine wave web
32 while the upper forming surface 57 defines the dimensions of the
upper surface of the sine wave web 32. Similarly, the left and
right forming surfaces 59 and 61 define the exterior dimensions of
the caps 34 and 36.
Although the present invention has been described with respect to a
particular tooling concept 40, other tooling concepts could also be
used. In addition, depending upon the complexity and geometry of
the sine wave spar 30 being formed, the tooling concept 40 may be
broken down into more or less individual tools to prevent tool
entrapment.
While the preferred embodiment of the invention has been
illustrated and described, it will be appreciated that various
changes can be made therein without departing from the spirit and
scope of the invention.
* * * * *